Amit Datye

Surface modification of Ni–Ti alloys for stent application after magnetoelectropolishing

The constant demand for new implant materials and the multidisciplinary design approaches for stent applications have expanded vastly over the past decade. The biocompatibility of these implant materials is a function of their surface characteristics such as morphology, surface chemistry, roughness, surface charge and wettability. These surface characteristics can directly influence the materials corrosion resistance and biological processes such as endothelialization. Surface morphology affects the thermodynamic stability of passivating oxides, which renders corrosion resistance to passivating alloys. Magnetoelectropolishing (MEP) is known to alter the morphology and composition of surface films, which assist in improving corrosion resistance of Nitinol alloys. This work aims at analyzing the surface characteristics of MEP Nitinol alloys by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The wettability of the alloys was determined by contact angle measurements and the mechanical properties were assessed by Nanoindentation. Improved mechanical properties were observed with the addition of alloying elements. Cyclic potentiodynamic polarization tests were performed to determine the corrosion susceptibility. Further, the alloys were tested for their cytotoxicity and cellular growth with endothelial cells. Improved corrosion resistance and cellular viability were observed with MEP surface treated alloys.

Extraction of Anisotropic Mechanical Properties From Nanoindentation of SiC-6H Single Crystals

Because brittle solids fail catastrophically during normal tension and compression testing, nanoindentation is often a useful alternative technique for measuring their mechanical properties and assessing their deformation characteristics. One practical question to be addressed in such studies is the relationship between the anisotropy in the uniaxial mechanical behavior to that in the indentation response. To this end, a systematic study of the mechanical behavior the 6H polytype of a hexagonal silicon carbide single crystal (SiC-6H) was performed using standard nanoindentation methods. The indentation elastic modulus and hardness measured using a Berkovich indenter at a peak load of 500 mN varied over a wide range of crystal orientation by only a few percent. The variation in modulus is shown to be consistent with an anisotropic elastic contact analysis based on the known single crystal elastic constants of the material. The variation in hardness is examined using a single crystal plasticity model that considers the anisotropy of slip in hexagonal crystals. When compared to experimental measurements, the analysis confirms that plasticity in SiC-6H is dominated by basal slip. An anisotropic elastic contact analysis provides insights into the relationship between the pop-in load, which characterizes the transition from elasticity to plasticity during nanoindentation testing, and the theoretical strength of the material. The observations and analyses lay the foundations for further examination of the deformation and failure mechanisms in anisotropic materials by nanoindentation techniques.

Dual-Scale Microstructure and Surface Analysis of Ti-Mo-Zr-Fe and Ti-Mo-Nb-Fe alloys for Orthopedic Implants

The increase in usage of prosthesis in patients has revealed evidence of in vivo fretting-assisted crevice corrosion of the mating surfaces, stress induced corrosion and fatigue failure, which lead to revision and bone loss every time surgery is performed. Titanium based alloys for the new generations of implant materials necessitate high strength-to-weight ratio, enhanced corrosion resistance, superior biocompatibility and excellent mechanical properties. Ti-13Mo-7Zr-3Fe (TMZF) and Ti-13Mo-13Nb-3Fe (TMNF) quaternary alloys address the aforementioned properties. The corrosion behavior, wettability, roughness and morphology of the alloys are determined in an effort to access their biocompatibility. The Modulus of elasticity and hardness of the alloys are measured by a nano-indenter.